The present invention relates in general to the art of earth boring and more particularly to a system for retaining the cutting elements in the cutter member body of an earth boring apparatus.
Cutting element life and efficiency are of prime importance in boring holes in the earth. For example, cutting element life and efficiency are important in drilling oil and gas wells and boring tunnels and raise holes. In general, the penetration rate is directly related to the condition of the cutter member and the condition of the cutter member is related to the condition and orientation of the cutting elements.
Cutter members having carbide insert cutting elements located in the body of the cutter member are generally utilized because of the ability of the carbide insert cutting elements to penetrate hard formations. The carbide inserts are mounted in a relatively soft metal forming the body of the cutter member. The most commonly used method of securing the inserts in the cutter member body is to provide cylindrical sockets in the cutter member body, to mold the inserts into a cylindrical shape, and to press-fit the inserts in the sockets in the cutter member body. The inserts are retained in the cutting member body by "hoop" tension generated when the insert is pressed into the relatively soft cutter member body. It has been discovered that when the inserts are press-fitted into the sockets, the sockets tend to be warped and a proper fit along the full length of the insertion is not obtained. Such inserts can become disoriented in the sockets during the earth boring operation and premature failure of the cutter can result. In addition, a rotary bit failure has been discovered known as cone peeling. This is a failure by cracking of the cone metal parallel to the bottom of the tungsten carbide insert in such a manner to remove the outer layer of the cone material and the inserts. This failure occurs near the bottom corner of the drilled holes for the tungsten carbide inserts.
Prior to the present invention the inserts were generally cylindrical sections pressed into radial cylindrical sockets in the cutter member. Since the cutter members have a circular cross-section, the interference fit at the lower portion of the socket caused expansion of the socket at the upper portion and loss of fit. The loss of fit resulted in the inserts becoming loosened in the cutter member body and premature failure of the cutter member. Cone peeling was also encountered. The present invention provides an improved fit throughout the length of the insert and promotes insert retention. cl BRIEF DESCRIPTION OF PRIOR ART
In U.S. Pat. No. 3,389,761 to Eugene G. Ott, patented Aug. 25, 1968, a rotary drill bit is shown including a rolling cutter having sintered metallic carbide inserts located in the cutter surface. The inserts include a plurality of alternate ridges and valleys on the side surface thereof that are sized to engage the walls of the holes in the rolling cutter whereby the inserts are retained in the rolling cutter against both longitudinal and rotational movement relative to the cutter.
In U.S. Pat. No. 2,097,037 to R. J. Kilgore, patented Oct. 26, 1937, a rock drill bit is shown in which hard metal inserts are tapered inwardly and are seated in tapered openings formed in the bottom of the bit. The tapered inserts do not bottom in the tapered openings and are accordingly held against being driven into engagement with the bottoms of the openings by the tapered side walls of the openings. The walls of the openings press forcibly against the inserts and tend to compress the inserts radially as well as prevent or resist inward movement of the inserts in their tapered openings.
In U.S. Pat. No. 3,311,181 to J. B. Fowler, patented Mar. 28, 1967, a bi-metal drilling tooth is shown. The drilling tooth includes a working section and a leading holding section.
In U.S. Pat. Nos. 3,461,983 and 3,513,728 to Lester S. Hudson and Eugene G. Ott jointly, patented Aug. 19, 1969 and May 26, 1970 respectively, an apparatus is shown that includes a member having a surface thereon exposed to an abrasive environment, the member having a relatively hard insert pressed into a hole in the member and having a hardfacing material on the surface of the member surrounding the insert. A method of manufacturing the apparatus is shown wherein the hole is plugged and hardfacing material is applied to the surface around the plug. After the hardfacing material has been permanently bonded to the surface, the plug is removed and the hard insert pressed into the hole to complete the apparatus.
In U.S. Pat. No. 3,599,737 to John F. Fisher, patented Aug. 17, 1971, a drilling tool or the like is shown with hardened metal inserts of molded sintered metal turned to cylindrical shape by centerless grinding and provided, prior to centerless grinding, with out-of-round abutment portions, the inserts being press-fitted into cavities in the cutter and the material of the cutter being staked to displace metal into engagement with the out-of-round abutment portions of the inserts to prevent axial and rotational displacement.
In U.S. Pat. No. 3,749,190 to Clarence S. Shipman, patented July 31, 1973, a rock drill bit having tapered carbide buttons projecting from its working face is described in which the buttons are retained in the bit by means of sleeves which are extruded into undercuts of the button holes and retain the carbide buttons in the drill bit by virtue of the sheer strength of the sleeves.